1. Field of the invention
The present invention is generally concerned with terminal blocks which mount on a rail and is more particularly directed to terminal blocks of this kind, usually called grounding blocks, designed to be used where the supporting rail serves as the main protection conductor for circuits which branch from it.
2. Description of the prior art
Known rails as usually employed for supporting electrical equipment are of two broad types: symmetrical rails, with a so-called hat-shape profile, and asymmetrical rails with a so-called G-shape profile.
All such rails, which are broadly U-shaped, have right-angle flanges featuring right-angle lips along their free edges so that equipment and terminal blocks may be attached to them.
In symmetrical rails, which further subdivide into numerous categories, specifically with regard to the depth and the thickness of the material from which they are made, these right-angle lips face outwards and thus extend away from each other, and are in the same plane.
In asymmetric rails the right-angle lips of the side flanges are directed inwardly, however, and so extend towards each other; they are not coplanar.
For mounting them on a rail of this kind, terminal blocks generally comprise, in a housing, a bearing member fixed relative to the housing and having two branches at least one of which is adapted to come into contact with the rail, to be more precise the right-angle lip on at least one of the flanges thereof, and, movable relative to the bearing member by a screw passing through the bearing member by means of a bore provided in it for this purpose, a clamping member also having two branches at least one of which is adapted to come into contact with the rail, to be more precise with the right-angle lip on at least one of the flanges thereof. In practise these terminal blocks are adapted to grip the right-angle lip on at least one of the flanges of the rail on which they are mounted, whereby they are fixed to the rail, through the intermediary of the bearing member and the clamping member at least one of which, and preferably both of which, is or are of metal to procure the necessary grounding contact.
To be more precise, in currently known terminal blocks, in order to achieve this clamping, the clamping member usually moves towards the head of the screw as this is screwed in and the faces on it designed to come into contact with the rail face generally towards the head of the screw so that they form hook faces, meaning faces adapted to interact with the right-angle lip on at least one of the flanges of a rail of this kind from below; conjointly, the faces through which the bearing member is adapted to come into contact with the rail usually face generally away from the head of the screw, in this case forming simple bearing faces, meaning faces adapted to interact with the right-angle lip on at least one of the flanges of the rail from above.
In other words, in currently known terminal blocks the bearing member usually acts in compression and the clamping member in tension.
This is the case, for example, with the terminal block that is the subject of German patent application No. 2 619 506 in which the massive clamping member also requires a special nut appropriately set into a cut-out in the clamping member, which is detrimental to the cost price of the assembly.
However, there have already been proposed terminal blocks in which the contact faces of the clamping member face generally away from the head of the screw, so that the clamping member, which is the movable part, is operative in compression whereas the bearing member, which is the fixed part, is operative in tension, its contact faces facing generally towards the head of the screw.
This is the case, for example, in the terminal block that is the subject of published French patent application No. 2 435 138.
However, in this terminal block, which incidentally does not comprise any housing, the clamping member is, like the bearing member, a massive part and is entirely contained within the internal contour of the bearing member, as a result of which it has extremely limited capacity of movement relative to the latter in the direction along the axis of the screw. Also, being massive, the clamping member prevents the provision of any form of hook face on the bearing member, between the branches thereof.
Because of this, the terminal block in question can only be fitted to a specific type of rail, in this instance a symmetrical rail with a hat-shape profile.
It cannot be mounted on an asymmetric rail having a G-shape profile.
In order to minimize the number of terminal blocks that have to be provided to cover all the range of rails that may be encountered, a terminal block should preferably be adapted to fit either onto a symmetrical rail, of whatever type, or onto an asymmetric rail.
This is the case, for example, with the terminal block that is the subject of published French patent application No. 2 410 207.
However, apart from the fact that the terminal block in question is of relatively complex construction, this embodiment necessitates the use only of a bearing member, a clamping member and a screw, but also of a nut which, engaged on the screw, cooperates with openings provided for it in the bearing member and in the clamping member; the clamping member moves not only in a straight line along the axis of the screw but also pivots, the assembly that is forms with the screw and the nut engaged on the screw being able to tilt relative to the associated bearing part; this tilting movement is necessary for the clamping member to be able to interact with the right-angle lip on at least one of the flanges of the rail from below, and also to avoid any possibility of interference between its movements during fitting to a symmetrical rail and during fitting to an asymmetric rail, and results in some uncertainty as to the final position of the clamping member when locked onto the rail, which is detrimental to the mechanical force with which it is retained on the rail and its centering relative to the rail.
Also, in the terminal block in question the rail is in practise gripped through the right-angle lip on only one of its flanges, there being merely a bearing or hooking relationship with the right-angle lip of the other flange.
As a result the terminal block assembly bears asymmetrically on the rail, further prejudicing the mechanical force with which it is retained on the rail with the result that the resistance of a terminal block of this kind to pulling off is not always totally satisfactory, especially where it is subject to twisting or torsional forces relative to the rail.
Finally, mistakes can occur when fitting the terminal block in question whereas, during removal, it may be difficult to disengage the terminal block from the rail.
A general objective of the present invention is an arrangement by which these disadvantages can be avoided and conferring other advantages.